To add to the answer given to question 3, there was a case where the most recent (2.1) firmware update worked on a jailbroken iPhone. I don't know if it was with a particular jailbreak software or multiple software packages but I did see people reporting that they updated as if the phone wasn't jailbroken and it worked with 2.1. I wouldn't count on this in the future though, you will probably have to wait.

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